[SPARK-14075] Refactor MemoryStore to be testable independent of BlockManager

This patch refactors the `MemoryStore` so that it can be tested without needing to construct / mock an entire `BlockManager`.

- The block manager's serialization- and compression-related methods have been moved from `BlockManager` to `SerializerManager`.
- `BlockInfoManager `is now passed directly to classes that need it, rather than being passed via the `BlockManager`.
- The `MemoryStore` now calls `dropFromMemory` via a new `BlockEvictionHandler` interface rather than directly calling the `BlockManager`. This change helps to enforce a narrow interface between the `MemoryStore` and `BlockManager` functionality and makes this interface easier to mock in tests.
- Several of the block unrolling tests have been moved from `BlockManagerSuite` into a new `MemoryStoreSuite`.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #11899 from JoshRosen/reduce-memorystore-blockmanager-coupling.